A public switched telephone network (PSTN) provides voice-grade telephone service in most parts of the world, connecting millions of telephones through a world-wide circuit-switched telephone network. To accommodate large numbers of telephone subscribers, a network is generally broken into local regions that are serviced by a central office (CO), which may be the physical building used to house telecommunications equipment. Each CO may include a Class 5 telephone switch.
A Class 5 switch is a large-scale telephone switch that can serve from several hundred to upwards of 100,000 subscribers, covering a city, a town, part of a city, or some other geographic region. A Class 5 switch provides telephone service to subscribers by providing a dial tone, local switching, access to the rest of the network, etc. Generally, a Class 5 switch routes calls by interpreting dialed digits. For example, a Class 5 switch may interpret dialed digits according to one or more dialing plans.
A dialing plan is a set of rules used by a switch to determine how each and every call that comes into the Class 5 switch is processed. One Class 5 switch can include many dialing plans, and each dialing plan is typically assigned to one or more subscribers on a particular switch. Over time, many dialing plans become unused, but remain stored in the switch's memory. Storage of unused dialing plans is undesirable because a Class 5 switch has limited memory, and memory upgrades can be very expensive. However, at present, unused dialing plans may be removed from a switch only through cumbersome, inefficient, and potentially unreliable processes.